How do monoclonal antibodies like trastuzumab function in cancer therapy?

Monoclonal antibodies such as trastuzumab are designed to specifically target the HER2 protein, which is overexpressed in certain types of cancers, particularly breast cancer. By binding to the HER2 receptor on the surface of cancer cells, trastuzumab helps to inhibit the signals that promote cell proliferation and survival. This targeted approach decreases the viability of the cancer cells, as well as their ability to grow and divide uncontrollably, leading to reduced tumor growth.

The other options describe different mechanisms of action that are not applicable to trastuzumab. For instance, while some treatments enhance immune response against tumors, trastuzumab's primary action is direct inhibition of the HER2 receptor. Initiating apoptosis is a cellular process often targeted by various therapies, but trastuzumab works mainly through receptor blockade and not directly inducing apoptosis. Finally, while angiogenesis inhibition is an important aspect of some cancer therapies, trastuzumab does not directly interfere with the formation of new blood vessels but rather targets the signaling pathway related to cell growth. Thus, the primary mechanism of action for trastuzumab is its ability to specifically target and inhibit the HER2 receptor on cancer cells.